In general, an image reproduction apparatus (i.e., a photocopier) reproduces images on an image-carrying medium by transferring toner or developer to the medium in relation to the characteristics of a given image. Such transfer is typically achieved through the use of a developing unit which places toner or developer on the image-carrying medium via a photoreceptor drum. To accomplish image transfer, the photoreceptor drum surface is first prepared by an electrophotographic image process to selectively accept toner in relation to the image characteristics. The developing unit then applies toner onto the photoreceptor drum via a developing roller. The toner applied to the photoreceptor drum is then transferred onto an image-carrying medium such as paper to reproduce the image. Further processing of the paper, for example, the application of heat, permanently adheres the toner to the paper.
In recent years, a rotary developing apparatus having multiple developing units has been proposed for color copiers, color printers and other image-forming apparatuses as disclosed, for example, in U.S. Pat. Nos. 4,782,360; 4,792,825; 5,258,819. In general, multiple independent developing units are housed in the rotary developing apparatus. Each of the multiple developing units is positioned around a cylindrical housing of the rotary developing apparatus, and each developing unit independently applies toner of a different color to a photoreceptor drum. To apply toner, only one independent developing unit is juxtaposed to the photoreceptor drum at a given time. Thus, for example, if four colors, such as yellow, magenta, cyan and black, are used, then four developing units (each containing one of these colors) are sequentially juxtaposed to the photoreceptor drum to apply toner of a particular color according to the characteristics of a desired image.
Each developing unit receives toner from a toner cartridge containing toner of a particular color. Although each toner cartridge may have the same toner capacity, depending upon the image characteristics, toner of one color may be consumed more quickly than toner of other colors. When one of the toner cartridges becomes empty, the operator must be notified so that he or she can replenish that toner or replace the empty toner cartridge with a new, full toner cartridge. Detection of an empty toner cartridge is known as "end detection" in the art of duplication machine technology.
Various attempts have been made to implement end detection. Attempts of particular relevance involve the use of light emitting and sensing devices. For example, Japanese Patent 61-180266 discloses the use of a light source and a light sensor mounted on the outside surfaces of a hopper to detect an empty condition in the hopper. However, this approach cannot practically be applied to a duplicating device that does not include a hopper. Japanese Patent 61-08/361,151,576 discloses an apparatus for detecting an empty condition in a toner cartridge in a duplicating device of the type wherein the toner cartridge is mounted to a rotary developing device. First and second pieces of optical fiber are placed on the inner bottom surface of the toner cartridge. When the toner cartridge is rotated adjacent to a light detection device, a light source emits light towards an end of the first optical fiber piece that faces the detection device. The emitted light is led to the other end of the first optical fiber and, if the cartridge is empty, the light is transmitted across a gap in the cartridge, and through the second optical fiber to a light sensor. On the other hand, if the cartridge is not empty, then there is no gap present, and the light is not transmitted to the second optical fiber. Thus, when the second optical fiber conveys the light to a light sensor, the toner cartridge is determined to be empty. The above-described optical sensing device requires a specially constructed toner cartridge, and the higher cost associated therewith is undesirable.
Japanese Patent 63-2087 discloses an optical toner end detection device which does not require a toner cartridge that has been specially adapted with additional elements. The system disclosed in this patent, however, requires a toner cartridge with a modified shape, i.e., a pinched bottom wall which provides a short cross sectional area. A light source and a light sensor are located across this pinched area for end detection. This system still requires a specially shaped toner cartridge.
Japanese Patent 2-114281 discloses an optical toner end detection system employing an ordinary toner cartridge. A light source and a light sensor are placed so as to transmit and receive light across the width of the toner cartridge as shown in FIG. 1. During an end detection interval, a brief burst of high intensity light is emitted by the light source. If light is detected by the light sensor, then the cartridge is determined to be empty. In addition, this reference discloses microprocessor-controlled flashing the light source.
In summary, the above-described attempts have required either a specially constructed toner cartridge with additional detection elements, a special toner cartridge shape, or a high intensity light source for accurate toner end detection. The additional elements lead to high manufacturing costs, the special shape hinders interchangeability of disposable toner cartridges, and the high intensity output shortens the life of the light source. In contrast, the current invention substantially overcomes these disadvantages without sacrificing accuracy in toner end detection.